Complex chemical composition of colored surface films formed from reactions of propanal in sulfuric acid at upper troposphere/lower stratosphere aerosol acidities

Particles in the upper troposphere and lower stratosphere (UT/LS) consist mostly of concentrated sulfuric acid (40-80 wt %) in water. However, airborne measurements have shown that these particles also contain a significant fraction of organic compounds of unknown chemical composition. Acid-catalyzed reactions of carbonyl species are believed to be responsible for significant transfer of gas phase organic species into tropospheric aerosols and are potentially more important at the high acidities characteristic of UT/LS particles. In this study, experiments combining sulfuric acid (H₂SO₄) with propanal and with mixtures of propanal with glyoxal and/or methylglyoxal at acidities typical of UT/LS aerosols produced highly colored surface films (and solutions) that may have implications for aerosol properties. In order to identify the chemical processes responsible for the formation of the surface films, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and ¹H nuclear magnetic resonance (NMR) spectroscopies were used to analyze the chemical composition of the films. Films formed from propanal were a complex mixture of aldol condensation products, acetals and propanal itself. The major aldol condensation products were the dimer (2-methyl-2-pentenal) and 1,3,5-trimethylbenzene that was formed by cyclization of the linear aldol condensation trimer. Additionally, the strong visible absorption of the films indicates that higher-order aldol condensation products must also be present as minor species. The major acetal species were 2,4,6-triethyl-1,3,5-trioxane and longer-chain linear polyacetals which are likely to separate from the aqueous phase. Films formed on mixtures of propanal with glyoxal and/or methylglyoxal also showed evidence of products of cross-reactions. Since cross-reactions would be more likely than self-reactions under atmospheric conditions, similar reactions of aldehydes like propanal with common aerosol organic species like glyoxal and methylglyoxal have the potential to produce significant organic aerosol mass and therefore could potentially impact chemical, optical and/or cloud-forming properties of aerosols, especially if the products partition to the aerosol surface.

Evaluation of transforming activity of cellular DNAs from different origins by NIH3T3 transfection test

The NIH3T3 cell transfection test, as first described by Cooper, has been optimized, then used to examine the transforming activity of genomic DNA extracted from eucaryotic cell lines commonly used for preparing vaccines or biopharmaceuticals. Accurate assessment of technical parameters of the test has led to improvement in reproducibility, while the demonstration of dose-effect relationships has allowed the definition of applications and limits for quantitative use. We have performed the direct assessment of transforming activity of cellular DNAs from cell lines widely used in biotechnology. In particular, we have shown that genomic DNA extracted from Vero, CHO or MRC5 cells, as well as from human or murine lymphoid cells, has no detectable transforming activity on NIH3T3 cells. Lastly, it has been demonstrated that acidic pH conditions are sufficient to destroy the major part--if not all--of the transforming activity of positive control DNAs.

Use of sulfonation method to determine DNA contamination of cell cultured monoclonal antibodies produced for human therapeutics

In the past few years, culture of transformed mammalian cells has been widely used to produce natural or recombinant molecules, as monoclonal antibodies (MAb) and cytokines. For therapeutic use, the cellular DNA level must be determined. A number of techniques have been developed to measure the DNA content, based on sequential extraction blotting and hybridization with a labeled DNA probe. The sulphonate marker has been recently introduced by PBS-Orgenics; it allows the determination of picograms (pg) quantities of purified DNA. However, it is not simple to measure in complex biological samples especially when a large amount of protein is present. In considering the following points: 1. Precautions in handling the samples at different steps of preparation; 2. Modifications of the original technique 3. Concentration of samples expected at very low level, we are able to dose up to 2 pg of contaminant DNA per mg of MAb with a satisfactory reproducibility and reliability. This level is required not only to qualify final MAb but also to evaluate the efficiency of the purification process. Efforts are being made to achieve a better sensitivity.